Filter device for the compensation of an asymmetric pupil illumination

ABSTRACT

The invention relates to a filter device for an illumination system, especially for the correction of the illumination of the illuminating pupil, including a light source, with the illumination system being passed through by a bundle of illuminating rays from the light source to an object plane, with the bundle of illuminating rays impinging upon the filter device, including at least one filter element which can be introduced into the beam path of the bundle of illuminating rays, with the filter element including an actuating device, so that the filter element can be brought with the help of the actuating device into the bundle of illuminating rays.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of, and claims priority under 35U.S.C. 120 to, U.S. application Ser. No. 13/215,910, filed Aug. 23,2011, which is a continuation of, and claims priority under 35 USC 120to, U.S. application Ser. No. 12/855,305, filed Aug. 12, 2010, which isa divisional of, and claims priority under 35 U.S.C. 120 to, U.S.application Ser. No. 11/722,631, filed Sep. 5, 2007, which is a NationalStage of International Application No. PCT/EP05/009165, filed Aug. 25,2005, which claims benefit of German Application No. 10 2004 063 314.2,filed Dec. 23, 2004. The contents of U.S. application Ser. Nos.13/215,910, and 12/855,305 are hereby incorporated by reference in theirentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a filter device for the compensation of anasymmetric pupil illumination of an illumination system, especially foran illumination system associated with a lithographic system.

2. Description of the Related Art

High demands are placed on illumination systems for lithographic systemsfor producing microelectronic or micromechanical components. Thisrelates both to systems which work as wafer stepper or as wafer scanner.Such an illumination system must illuminate an object, which istypically a mask, in a field plane of the illumination system in ahomogeneous manner. In addition to this requirement, there is also ademand for the angular distribution of the illumination in the fieldplane, which on its part is associated with the illumination of the exitpupil of the illumination system. For a lithographic system, the exitpupil of the illumination system coincides with the entrance pupil of adownstream projection objective. That is why it is necessary to arrangethe illumination characteristics of the exit pupil in an adjusted mannerin order to introduce the largest possible amount of light into theprojection objective, to fulfill the requirement of telecentricity inthe image plane of the projection system and in order to achieve themost even possible imaging of the mask structures.

For evening the illumination of a field in the field plane, illuminationsystems are known in which a rod-like optical integrator is used.Depending on the operating wavelength, the material of such a rod-likeoptical integrator is adjusted. It can consist for example of quartzglass or a crystalline material such as calcium fluoride. The effect ofsuch a rod-like optical integrator is disclosed for example in U.S. Pat.No. 5,675,401, US Pat. No. 2004/012766, EP 0867772, U.S. Pat. No.6,236,449 or EP 0747772. It provides that as a result of the pluralityof total reflections of the light coupled into the rod-like opticalintegrator, a thorough mixture of the illumination light is achieved onits outside surfaces. The total reflection is not completely withoutlosses due to the residual roughness of the surfaces of the rod jacket.

An undesirable asymmetry of the illumination of the exit pupil occurs inscanners due to the rectangular cross section when using rod-likeoptical integrators. Light rays which extend predominantly parallel tothe narrow side are reflected more frequently and are thereforeattenuated more strongly. This asymmetry leads to an energeticallyelliptic pupil profile and is referred to below as ellipticity. In orderto avoid an asymmetry of the illumination, a rod-like optical integratoris known from U.S. Pat. No. 6,733,165 which has such an aspect ratiobetween width and height, that the number of reflections and thus thetotal reflection losses on its side surfaces are set in such a way thata predetermined distribution of the luminous energy is produced in theangular space on the output surface of the glass rod. Thedisadvantageous aspect in this solution according to U.S. Pat. No.6,733,165 is that only elliptical asymmetries can be corrected.

Furthermore, adjustable symmetric pupil filters are known. U.S. Pat. No.6,535,274 for example discloses a filter arrangement in which at leasttwo symmetrical filter elements are turned against each other and anadjustable, but symmetrical, intensity filter for filtering the pupilillumination is realized. Pupil filters which are disclosed in U.S. Pat.No. 6,535,274 allow producing or correcting an ellipticity of thedistribution of the illumination angle in the object plane by settingthe respective transmission in the area of the pupil plane of theillumination system of a projection exposure system. The correction of acomplex asymmetry is not possible.

U.S. Pat. No. 6,636,367 shows an illumination system in which changes inthe distribution of the angle of illumination can be made throughcontrolled movement of the pupil filter which is arranged in the regionof the pupil plane. The pupil filter is arranged as a rotatable elementwhich has a transmission distribution which is non-rotation-symmetricabout the rotational axis. Ellipticity can thus also be set incombination with a rod as an integrator.

From US 2003/0076679 an illumination system is known which includes atleast one diffraction grating in the light path from the light source tothe plane in which the structure-bearing mask is arranged. Thediffraction grating is used to reflect light at different anglesrelative to the optical axis.

Illumination systems have further become known with an opticalintegrator in the light path from the light source to the plane in whicha structure-bearing mask is arranged, e.g. from U.S. Pat. No. 5,731,577,U.S. Pat. No. 5,461,456, U.S. Pat. No. 6,333,777 or EP 0849637.

The optical integrators according to U.S. Pat. No. 5,731,577, U.S. Pat.No. 5,461,456, U.S. Pat. No. 6,333,777 or EP 0849637 includes facettedelements.

Field filters are further known for improving the uniformity of theillumination of a field in the field plane, i.e. filter devices whichare positioned closer to a field plane than a pupil plane of theillumination system. EP 1 291 721 discloses a field filter in which theorientation of lamellae-like elements can be set substantially in theambient environment of the field plane and thus a local blockade effectin the beam path can be achieved. This filter does not allow howevercorrecting the angular spectrum of the illumination of the field planeand thus an asymmetry concerning the intensity of the illumination ofthe exit pupil of the illumination system.

The disadvantageous aspect in all filter elements known from the stateof the art is that they are limited to the correction of certainasymmetries or asymmetric aberrations of the pupil, e.g. to thecorrection of elliptical asymmetries. The known pupil filters are notsuitable for correcting complex asymmetries or asymmetric aberrations inthe pupil illumination.

What is needed in the art is a pupil filter with which the disadvantagesof the state of the art can be overcome and with which it is especiallypossible with the pupil filter in accordance with the invention tocorrect any asymmetry of the illumination of an exit pupil or a pupilconjugated to the exit pupil. This relates especially to illuminationsystems in which the asymmetries occur in the illumination of the exitpupil which include not only elliptical portions.

SUMMARY OF THE INVENTION

In accordance with the present invention, a filter device associatedwith the exit pupil includes a plurality of filter elements, with eachof these filter elements projecting substantially in the radialdirection into the beam path of a bundle of projecting rays which passesthrough the illumination system from the light source to the plane inwhich a structure-bearing mask such as a reticle is arranged and thusproduces a shadow effect. The degree of the blockade effect, i.e. theshading in the beam path of the light, can be set individually for eachfilter element.

A crown-like arrangement of the filter elements is possible, meaningthat they are introduced from the outside circumference of the beam pathin the direction towards the center of the beam path. The shadow effectcan be produced either by setting the insertion depth in the radialdirection or by an orientation of the asymmetrically formed filterelements in the beam path.

It is further possible that the filter device does not influence thepupil size and thus the σ-value of the illumination of the exit pupil.This is achieved in such a way that the filter elements are chosen withrespect to their dimension and arrangement density in such a way thatthe maximum shadow width of each filter element is only 1 to 5% of thedistance between two filter elements in the region of the outsidecircumference of the beam path. It follows from this that the filterelements are provided with a rod-like configuration, i.e. their lateraldimensions are typically smaller than the dimensions in the radialdirection, i.e. the direction of insertion into the beam path. On theother hand, the preferred dimensions of the filter elements must bechosen in such a way that each filter element influences the pupilillumination in a certain local area. Local area shall be understood asa number of percent of the pupil surface. In order to achieve thehighest possible adjusted correction of the asymmetry of the exit pupilof the illumination system, a filter device with more than 20 filterelements can be used.

In addition to the possibility as already explained above to determinethe local shading effect of a filter element by setting the insertiondepth in the radial direction into the beam path, an additional oralternative possibility is to configure a filter element in anasymmetric fashion, e.g. in the form of a lamella, and to control theangle of incidence, i.e. the orientation, of the filter element in thebeam path. The filter elements can be configured as triangular thinpaddles. They can then be oriented in two extreme positions. On the onehand, the beam of the beam path will only impinge on the narrow side ofthe triangular paddle. In this case the blockade effect and thus alsothe shadow casting is minimized by the filter element. On the otherhand, the paddle can also be turned completely into the beam path, as aresult of which the shadow casting is maximized. The triangular shapewhich can taper in an acute angle is used to successively reduce theblockade effect by the filter element in the direction of the center ofthe beam path. The setting of the shadow casting via the orientation ofthe filter element can also be combined with the setting of the radialinsertion depth.

In the configuration of the outer form it is possible to provide thefilter element with partial transparency at least in partial areas or toprovide the same as an unsupported net structure. In the geometricalconfiguration there is thus freedom to configure a filter element insuch a way that by setting the radial insertion depth and itsorientation the local shading effect can be adjusted as individually aspossible. The actuating elements for achieving the desired setting andorientation can be chosen at the discretion of the person skilled in theart. This can be achieved for example by stepper motors, piezoelectricelements or slip-stick drives. In addition, the entire device can beprovided with a configuration which is rotatable about its center inorder to compensate the location-discrete effect caused by the limitednumber of actuating elements.

The filter device can be arranged in such a way in the ambientenvironment of the exit pupil or a pupil conjugated with the exit pupilin the illumination system that at least part of the shadow casting ofthe filter elements in the pupil plane has the effect of a partialshadow. The desired influence on the asymmetrical properties of thepupil illumination can thus be achieved in the most precise possible wayand with little side-effects on other pupil parameters such as the size.The maximum distance of the filter device to the pupil plane is chosenin such a way that the partial shadow of a filter element reaches thecircumferential region of the beam path at most up to the center of thepartial shadow of the adjacent filter elements. It follows from thisthat the maximum distance is influenced by the predetermined angulardistribution in the pupil illumination.

A larger distance chosen beyond this threshold would lead to the effectthat the partial shadow regions which can be associated to an individualfilter element would reach into the partial shadow region of the one butnext filter element, and thus an individual adjustment of the asymmetrycorrection would become more difficult. In the present application, aregion Δz in the direction of the light is understood as being close tothe pupils, which region fulfills the condition that the partial shadowsof the individual filter elements overlap half at most in thecircumferential region of the beam path. The filter element is arrangedclose to the pupil in the case when it lies within the region Δz.

The limits of the region Δz are predetermined on the one hand by thepupil plane per se and on the other hand by the maximum distanceΔz_(MAX). The maximum distance Δz_(MAX) is a distance from the pupilplane in which the partial shadows of the respective one but the nextfilter elements just contact each other in the circumferential region ofthe beam path.

The partial shadows of the individual filter elements are created byshadow casting. Shadow casting shall be understood in this applicationas the shadings occurring in a plane arranged directly behind the pupilfilter.

In a second aspect of the invention, a filter device for an illuminationsystem is provided which includes at least one filter element which canbe introduced into the illumination beam path of an illumination systemin different positions, with the filter element including a sensor fordetermining the intensity values. The sensors allow the measurement ofintensity values in the illumination beam path along the filter elementin a position-resolved way. The influence of the filter element on theillumination properties (i.e. the illumination in a field plane of theillumination system) can be obtained from the measured intensity valuesof the filter element. With the help of the filter element in accordancewith the invention, it is possible to measure ellipticity,telecentricity and transmission of the illumination as illuminationproperties of the illumination.

The measured intensity values can be read into a control device and canbe compared for example with the setpoint values of an illumination tobe achieved in the field or pupil plane. These setpoint values lead tosetpoint positions for the filter element to achieve the illumination inthe field and/or pupil plane. If the filter device with the filterelements is used as a pupil filter, a comprehensive calibration of thefilter element is thus avoided by such a further developed embodiment.Such a calibration is necessary because the configuration of the filterdevice depends very strongly on the illumination mode, especially theposition of the filter elements for achieving a certain illumination inthe field and/or pupil plane. The type of illumination is designated asthe illumination mode, e.g. an annular or quadropolar illumination.Moreover, a precise adjustment of the filter apparatus with respect tothe illumination system is no longer required in order to ensure thatthe actuating positions as measured on delivery are still valid evenafter the installation of the correction system or when and it isexchanged at the customer's location.

The sensors for determining the intensity values can be configured aspower sensors, e.g. photodiode sensors. The sensors can be arranged atone end of a filter element configured in the form of a rod.

The sensors can be connected with a control device in such a way thatsignals can be exchanged via electric lines or radio link between thesensors and the control device.

If the sensor is arranged as described above at one end of a rod-likefilter element, the light intensity which is absorbed by the insertionof the rod-like filter element into the illumination beam path isdetermined by integration of the measured values which are determinedwhen the rod-like filter element is moved in a quasi continuous way froma certain position outside of the illuminated region into the same andthe intensity is measured depending on the position of the sensor.

In a second, further developed embodiment a rod-like filter element canbe covered completely with quasi punctiform energy sensors, e.g.photodiode sensor lines or CCD (Charge-Coupled Device) lines. Thisembodiment has the advantage that the measurement of the absorbedintensity which depends on the location of the rod-like filter elementcan occur when the filter element is moved into the illuminating beampath.

A successive insertion as in a rod-like filter element with only onesensor attached to the end of the rod-like element is not necessary.

Since the energy sensors are only needed for determining the exactposition of the filter element, it is provided for in a furtherdeveloped embodiment in order to protect the sensors from permanentradiation by the same illumination mode that the filter element isrotatable about its own axis in order to position the sensors in theshadow of the filter element by rotating the filter element by 180°after the performed measurement and thus to protect the sensors fromdamage.

If the filter element, and especially the rod-like filter element in afurther developed embodiment as described above, is provided withsensors, it is possible to measure the share of light as absorbed by thefilter element in a location-resolved way with respect to a freelychosen but fixed system of coordinates along the filter element. Basedon this information it is possible to perform a calculation of thesetpoint position of the filter element for the set illumination mode inorder to thus obtain the desired state of corrections of field and/orpupil illumination. In the case of a field correction, the individualfilter elements are moved into the light distribution in the field forcorrecting the scan-integrated intensity.

By attaching sensors to the filter element, it is further possible toalso determine the edge of the pupil in that the edge is measured in thetransition of the sensor into the illuminated area.

This enables a very precise adjustment of the correction unit relativeto the illumination system.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention,and the manner of attaining them, will become more apparent and theinvention will be better understood by reference to the followingdescription of embodiments of the invention taken in conjunction withthe accompanying drawings, wherein:

FIG. 1 shows a schematic overview of a projection exposure system;

FIG. 2 shows an arrangement of radially displaceable filter elements ofa pupil filter in accordance with the invention;

FIG. 3 shows the pupil filter of FIG. 2 with differently set filterelements;

FIG. 4 shows a single filter element;

FIG. 5 shows a configuration of the filter device with radially orientedfilter elements which are rotatable about their longitudinal axes;

FIG. 6 shows a three-dimensional view of a rotatable filter element;

FIG. 7 shows a three-dimensional view of a filter element with atransparent region;

FIG. 8 a shows the relevant optical components of a projection exposuresystem;

FIG. 8 b shows the shadings in detail for a projection exposure systemaccording to FIG. 8 a;

FIG. 8 c shows the cross section of the pupil filter and theillumination in the plane in which the filter apparatus is arranged;

FIG. 8 d shows the cross section of the illumination in the pupil plane;

FIGS. 9 a, 9 b show the corrected and uncorrected illuminations of theexit pupil of a projection exposure system as shown in FIG. 8 a fordipolar illumination; and

FIG. 10 shows an embodiment of a filter apparatus with quasi punctiformsensors applied to the individual rod-like elements.

Corresponding reference characters indicate corresponding partsthroughout the several views. The exemplifications set out hereinillustrate embodiments of the invention, and such exemplifications arenot to be construed as limiting the scope of the invention in anymanner.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, and more particularly to FIG. 1, there isshown a projection exposure system for microlithography which isdesignated in its entirety with reference numeral 1. The projectionexposure system is used for transmitting a structure on a reticle 2 ontothe surface of a wafer 3. The light source for the projection exposuresystem 1 is a UV laser 4, e.g. an ArF excimer laser with a wavelength of193.3 nm. A bundle of illumination rays emitted by the same meets atfirst the illuminating optics 6. The beam path of the bundle 5 ofilluminating rays is only indicated between the UV laser 4 and theilluminating optics 6 for reasons of clarity of the illustration. Theilluminating optics 6 are shown in FIG. 1 only schematically in the formof a block and can include a number of optical modules such as a zoomobjective, diffractive optical elements or an optical integrator forhomogenizing the bundle 5 of illuminating rays.

When passing through the illuminating optics 6, the bundle 5 ofilluminating rays passes through a filter device which is arranged in orclose to a pupil plane 13 and which will be designated below as pupilfilter 7. The pupil filter is configured in accordance with theinvention and will be described below in closer detail. In the presentembodiment, the pupil filter 7 is arranged before the pupil plane 13.The position of the pupil filter 7 is also referred to below as thefilter plane. The bundle 5 of illuminating rays then illuminates thereticle 2. The structures of the reticle 2 are projected with the helpof projection optics 8 onto the surface of the wafer 3. The projectionoptics 8 can be composed of a plurality of lenses and/or mirrors.

A selected bundle of projection light which passes a central objectpoint on the reticle 2 and is guided with the projection optics 8 isprovided in FIG. 1 with the reference numeral 9 and is extended a bitinto the opposite direction for clarifying the path of the projectionrays, i.e. in the direction towards and into the illuminating optics 6.The reticle 2 lies in the object plane 10 of the projection optics 8which is indicated in FIG. 1 by a broken line. The wafer 3 lies in animage plane 11 of the projection optics 8 which is also indicated by abroken line. A pupil plane 12 of the projection optics 8 is alsoschematically indicated in FIG. 1. It is conjugated in the illuminatingoptics 6 relative to the pupil plane 13. The pupil plane 12 is alsodesignated as the entrance pupil of the projection optics 8.

The optical axis of the projection exposure system 1 is also indicatedin FIG. 1 with the broken line and provided with reference numeral 14. Apartly transparent optical plate 40 is arranged in the illustratedembodiment of a projection exposure system in the beam path between theUV laser 4 and the illuminating optics 6, which plate reflects a smallportion of the bundle 5 of illuminating rays and transmits thepredominant portion (which is usually more than 99%) of this luminousbundle. The beam path of the bundle 5 of illuminating rays which passesthrough the optical plate 40 is only continued a small amount because itis not of further interest.

The reflected portion of the bundle 5 of illuminating rays after theoptical plate 40 which is also shown in a broken line is projected ontoa two-dimensional CCD array 16 by way of projection optics 15. The CCDarray is in connection with a control device 18 via a signal line 17shown in a dot-dash line. The control device 18 controls a drive device20 via a signal line 19 which is also shown in a dot-dash line. Thedrive device 20 can drive the pupil filter 7 or individual elements ofthe pupil filter for asymmetry correction via a drive connection 21which is also shown in a dot-dash line.

A detection device 30 which can be used alternatively or in addition tothe CCD array 16 for measuring the distribution of the illuminatingintensity and illuminating angle of the projection bundle 9 in theobject plane 10 is shown in FIG. 1 in an inactive position outside ofthe path of the projection rays. The detection device 30 can be movedinto the beam path of the optics by way of a drive device (not shown)perpendicularly to the optical axis 14 (as illustrated by the doublearrow 31) after the removal of the reticle 2 in such a way that anentrance opening 32 lies in the object plane 10 through which aprojection bundle (e.g. projection bundle 9) usually illuminating thereticle can enter the interior of the detection device 30.

The detection device 30 is connected via a flexible signal line 33 witha control device 34 which on its part is in connection with the controldevice 18 by a signal line 35 shown with a dot-dash line.

It can be provided for in a further alternative embodiment of theinvention that the detection device 30 be provided for measuring theilluminating intensity in the image plane 11 of the projection optics 8in which the wafer is also arranged.

FIGS. 2 to 7 show below the configuration of an embodiment of a filterapparatus which can be used as a pupil filter 7 for the correction ofasymmetry.

FIG. 2 shows a first embodiment of a filter apparatus of the pupilfilter 100. It includes filter elements that are individuallyadjustable. The filter device can be arranged in the vicinity of theexit pupil or a pupil conjugated to the exit pupil. The individualfilter elements can intervene from the outside into the beam path. Eachof the filter elements 103 is provided in the present embodiment withthe rod-like configuration. Its dimensions in an azimuthal directionwhich stands perpendicular to the radial direction are clearly smallerthan the radial extension of the filter elements 103.

In the pupil filter 100 as shown in FIG. 2, the radial direction R andthe azimuthal direction φ are entered.

In a first embodiment of the invention the filter elements 103 areinserted depending on the required correction of asymmetry from theoutside circumference 104 of the filter device 100 in the directiontowards the optical axis HA of the beam path. In the illustratedembodiment however, the direction of insertion of the filter element 103coincides with the radial direction R. Moreover, the dimensions d of thefilter elements 103 are chosen preferably smaller in the azimuthaldirection φ than the distance D between two single adjacent filterelements 103.1,103.2. The distance in the region of the outsidecircumference 104 of the filter device 100 is regarded as the distance Dof two filter elements 103.1, 103.2. A lateral extension d of 1 to 5% ofthe distance D of the filter elements with respect to each other isespecially preferable, i.e. when the distance D of a first filterelement 103.1 from the adjacent second filter element 103.2 is 100 mm,then the width d of the individual filter elements 103.1, 103.2 is 1 mmto 5 mm. When choosing such a dimensioning, the desired local intensityadjustment for the correction of asymmetry of the pupil illumination canbe adjusted by way of the individual settings of the filter elements103.1, 103.2 of the filter device without this having influence on thepupil size per se.

In the embodiment of the invention as shown in FIG. 2, the pupilillumination is corrected or set in such a way that every single filterelement 103 can be inserted to a differently large extent in the radialdirection R into the filter device. In order to enable setting theinsertion depth individually in the radial direction each filter element103 is associated with an actuating element 113. This actuating element113 can be used for separately setting the insertion depth T in theradial direction R into the beam path for each filter element. FIG. 4shows an individual rod-like filter element 103 in conjunction with anactuating element 113 which includes a drive for a linear movement, i.e.a displacing movement in the radial direction R of the filter device100. It is understood that also embodiments of the invention arepossible in which only a part of the filter elements includes anactuating element for displacement in the radial direction and anotherpart is provided with a fixed configuration.

In the filter device 100 as shown in FIG. 2, the maximum depths T_(MAX)are shown with the dot-dash line 132 by which the individual filterelements 103 can be displaced in the radial direction towards the centerM of the filter device 100, especially the pupil filter.

As is shown in FIG. 2, the maximum depths T_(MAX) are chosen in such away that they nearly reach the optical axis HA of the beam path as shownin the present embodiment. It is possible that the individual filterelements 103 neither overlap nor touch each other when they have beendisplaced up to the maximum depth T_(MAX) into the filter device 100.The shadings that can be set at most are predetermined for each of thefilter elements 103 by the maximum depth T_(MAX).

FIG. 3 shows a possible setting for the filter device in accordance withthe invention according to FIG. 2. The same components as in FIG. 2 bearthe same reference numerals. It is shown that the individual filterelements 103 project to a differently large extent into the crosssection 106 of the bundle of illuminating rays in the plane in which thefilter device is arranged (FIG. 3 shows cross section 106 morespecifically as cross section 106.1). As is shown in FIG. 1, the bundleof illuminating rays passes through the illumination system from thelight source to the plane in which the structure-bearing mask (e.g. thereticle) is arranged. In the present case, the bundle of illuminatingrays has a circular cross-section 106 without being limited to the same.The circular cross-section has a circular surrounding edge 107.

The cross section 106 of the bundle of illuminating rays is shown inFIG. 3 with contour lines 109. The density of the contour lines 109 is ameasure for the change of the light intensity in the cross section ofthe ray bundle. It applies in general in the illustrated figures thatthe narrower the light intensity, the faster the light intensitydecreases.

A parabolic profile is obtained in the radial direction R in the case ofa circular illumination φ.

By introducing rod-like filter elements into the illumination, theillumination is cut off more strongly in the direction of the circulararc and thus a rotation-symmetric illumination is achieved. Thecircularity of the cross section 106 of the beam path in FIG. 3 shall beregarded only in illustrating manner and not in a limiting manner,because others are also used in lithographic systems.

FIG. 5 shows a further advantageous embodiment of the filter device 200in accordance with the invention. In this case, the shadings in the beampath of the bundle of illuminating rays are not achieved by displacingthe filter elements in the radial direction as in the filter device asshown in the FIGS. 2 to 4. Instead, this is achieved by controlling theorientation of the filter elements in the beam path of the bundle ofilluminating rays. For this purpose, the filter elements 203.1, 203.2and 203.3 of the filter device 200 are provided with an asymmetricconfiguration. Asymmetric configuration shall be understood in such away that the part of a filter element 203.1, 203.2 and 203.3 projectinginto the beam path has a different extension in a first direction 202.1perpendicular to the radial direction R as compared with the seconddirection 202.2 which stands perpendicular to the first direction 202.1.This is shown to the filter element 203.3. The filter element 203.3shows both the first direction 202.1 and the second direction 202.2. Asis shown in FIG. 5, the filter element can be arranged in the form of alamella. The lamella can be triangular and can taper with an acuteangle. The setting of the individual filter elements 203.1, 203.2, 203.3as shown in FIG. 5 is made by rotation of the filter element about arotational axis RA.1, RA.2, RA.3 in which each filter element extends inthe radial direction R towards the centerpoint M of the filter device200. The different filter elements 203.1, 203.2, 203.3 are shown in FIG.5 in different orientations. The minimal shadow casting is shown for afirst filter element 203.1, which means that the projection exposurebundle meets the narrow side of the filter element 203.1. A secondfilter element 203.2 has been turned in comparison with the filterelement 203.1 about 45° about the axis RA.2, as a result of which theshadow casting of the filter element 203.2 increases over the shadowcasting of the filter element 203.1 in a plane which is arranged behindthe pupil filter. Shadow casting shall be understood within the terms ofthis application as the shading occurring in a plane arranged directlybehind the pupil filter. A third filter element 203.3 shows the fullturning with an angle of 90° in the beam path, i.e. the maximumdimension of the filter element blocks the radiation and the maximumpossible local shading is achieved.

FIG. 6 shows a three-dimensional view of an individual filter element203, as shown in FIG. 5.

The filter elements 203 shows in FIG. 5 a triangular shape with thelength L which is far longer than the width B and a thickness D. Inaccordance with the invention, the extension in a first direction whichis designated in the present case as the X-direction is substantiallylarger than in a second direction which is designated in the presentcase as the Y-direction.

FIG. 6 also shows the local rotation axis RA. The filter element 203 canbe rotated about the same for casting different shadows in a planebehind the pupil filter. The figure further shows the center M of thepupil filter and the actuating element which is configured here aselectromotor 231 for moving the filter element 203 about the rotationaxis RA.

A combination of a different configuration of the filter elements whichcan both be inserted radially into the beam path and can be oriented inthe same is possible, i.e. a combination of the embodiments according toFIGS. 2 to 4 and 5 to 6. There is also the possibility to arrange thefilter element not only as a solid body as shown in FIG. 6 but also toconfigure the same completely or in certain areas in a partlytransparent way.

Such a filter element is shown in FIG. 7. The same components as in thefilter element shown in FIG. 6 are designated with reference numeralswhich are increased by 100. A first region 305.2 is configured as asolid body and a second region 305.1 in a partly transparent way withrods 307.

The partial transparency can be produced by a sufficiently fine grating.Self-supporting gratings can be used in order to avoid reducing thepartly transparent effect by an additional boundary as in the embodimentaccording to FIG. 7.

FIG. 8 a shows an illumination system with a pupil filter 552 inaccordance with the invention for the correction of asymmetry of thepupil illumination. Although the individual optical components are shownin more detail in the illumination system as shown in FIG. 8 as comparedwith FIG. 1, the illumination system is still shown in a highlysimplified way.

The illumination system which is designated in total with referencenumeral 510 includes a light source 512 which is configured as anexcimer laser which generates monochromatic and strongly (but notcompletely) collimated light with a wavelength in the ultravioletspectral range of 193 nm or 157 nm for example. The light source canemit polarized light.

The light generated by the light source 512 is expanded in a beamexpander 514 into a rectangular and substantially parallel bundle ofrays. The beam expander 514 can concern an adjustable mirror arrangementfor example. The now expanded light then passes through a first opticalraster element 516 which can concern a diffractive optical element witha two-dimensional raster structure for example, as described in EP0747772 A1. The first optical element is used to introduce entendue orso called light conductance value into the system. The laser beam isdiffracted at each location of the diffractive optical element in acertain angular range which can lie between −3° and +3° for example. Theangle radiation characteristics of the diffractive optical element isdetermined by the design of the diffractive surface structure on thediffractive optical element, so that a respective intensity distributionsuch as a dipolar or quadrupolar distribution is provided in a pupilplane 550 of a zoom-axicon objective. The light originating from thelight source 512 is converted into a circular, annular or quadrupolardivergence distribution with said first optical raster element 516 forsetting the divergence distribution. If an illumination is desired inthe presence of a polarized light source such as a polarized laser, adepolarizer can be used in order to depolarize the laser light. Such adepolarizer consists for example of a first camera wedge made of adouble-refracting material and a second camera wedge which compensatesthe angle introduced by the first camera wedge and is made ofdouble-refracting or non-double-refracting material.

The first optical raster element 516 is arranged in an object plane 518of a zoom-axicon objective 520 with which the distribution ofilluminating angle can be changed and thus the illumination in the pupilcan be formed further. For this purpose, the zoom-axicon objective 520includes two axicon lenses 522, 524 which form a pair and aredisplaceable relative to each other.

The axicon lenses 522, 524 can include two conical lenses. By setting anair separation between these two conical lenses it is possible toachieve a shifting of the light energy to the outer regions. A hole or aregion without light is produced in the middle around the optical axis(i.e. a so-called annular sectioning) in the illumination in the pupilplane.

The illumination system as shown in FIG. 8 a includes a pupil plane 550between the zoom-axicon objective and the axicon lenses 522, 524, whichpupil plane is conjugated to the pupil plane 530 and conjugated to theexit pupil 560 of the illumination system 510. The pupil filter 552 inaccordance with the invention is arranged in or close to this pupilplane 550 for correcting the asymmetry or asymmetric aberrations. Thepupil filter for correcting asymmetry or asymmetric aberrations can alsobe arranged in or close to another pupil plane present in the system. Inthe present case, the pupil filter 552 has a distance Z to the pupilplane 550. The distance Z lies within the region Δz, with the region Δzbeing defined on the one hand by the pupil plane 550 as the limit and onthe other hand by the distance Δz_(MAX). The distance Δz_(MAX) is thedistance at which the partial shadows of the individual filter elementsoverlap half at most in the circumferential region of the beam path.

FIG. 8 b shows this in closer detail. The same components as in FIG. 8 aare designated with the same reference numerals. The bundle 513 ofilluminating rays which starts out from the light source (not shown) andmeets the first optical raster element 516 can clearly be recognized.The object plane 518 and the pupil plane 550 are shown. In theconfiguration as shown in FIG. 8 b, the filter device (i.e. the pupilfilter 552 in accordance with the invention which is shown by way ofexample in FIG. 3 and is designated there with reference numeral 100) isarranged before the pupil plane at a distance Δz=Z_(MAX) in a plane 553.The distance Z_(MAX) in which the filter device 552 can be arrangedspaced from the pupil plane 550 is given in such a way that the partialshadows 580.1, 580.2 of the respective filter elements 103.1, 103.2(FIG. 3) of the filter device 552 overlap half at most in the pupilplane 550. The marginal rays of the ray bundles 582.1 and 582.2 aredesignated with reference numerals 582.1.1, 582.1.2, 582.2.1, 582.2.2.

FIG. 8 c shows the filter apparatus 100 which is identical to the filterapparatus 552 in FIGS. 8 a and 8 b in the plane 553 in a top view. Thesame components as in FIG. 3 are provided with the same referencenumerals. The individual filter elements 103.1, 103.2 are shown. Thefigure also shows the cross section of the illumination 106.2. Theillumination 106.2 as shown in FIG. 8 c in the plane 553 is annular andis limited by the edges 107.1 and 107.2.

When the plane 553 is arranged at a distance Δz=Z_(MAX) relative to thepupil plane 550, the illumination 106.3 as shown in FIG. 8 d is obtainedin the pupil plane 550 in the cross section when using the illuminationas shown in FIG. 8 c. The effect of the partial shadows can clearly beseen, which leads to a flattening of the illumination in thedistribution of intensity of the illumination 106.3 in the pupil planewith a number of minimums 198.1, 198.2 and maximums 199.1, 199.2corresponding to the number of the filter elements 103.1, 103.2. Thesame components as in FIG. 8 c are designated with the same referencenumerals. Z_(MAX) is designated as the distance which the partialshadows of the respective filter elements of the filter device overlaphalf at most in the pupil plane.

A second objective 528 is arranged in the beam path of the illuminatingsystem according to FIG. 8 a behind the zoom-axicon objective 520, whichsecond objective projects the first pupil plane 550 onto a second pupilplane 530. A second optical raster element 532 is arranged in saidsecond pupil plane 530 which may concern an optical element in themanner of a microlens array or honeycomb condenser. The second opticalraster element 532 can be used to increase the divergence of the lightcoming from the second objective 528 in a purposeful way dependent onthe direction, e.g. in order to achieve a rectangular illumination ofthe field plane 536. The filter element can be arranged before thisfield-generating raster element in order to achieve the most even effecton all field points.

As an alternative to the arrangement in or close to the pupil plane 550,the filter device 552 in accordance with the invention can also bearranged in or close to a second pupil plane 530, for example betweenthe second objective 528 and the second pupil plane 530.

In FIG. 8 a, the raster element 532 is the last optical element in theillumination system 510 which changes the entendue or the so calledlight conductance value. The entendue to be achieved at most by theillumination device 510 is thus reached behind the raster element 532.The entendue is only approximately 1% to 10% of the entendue between thefirst optical raster element 516 and the second optical raster element532 which can be achieved behind the second optical raster element 532.This means that the light which passes through the second objective 528is still collimated relatively strongly. The second objective 528 cantherefore be configured in a very simple and inexpensive manner.

In the direction of the light propagation behind the second opticalraster element 532, a third objective 534 is arranged in whose fieldplane 536 is arranged a known mask device 538 with adjustable knifeedges. The mask device 538 determines the shapes of the region which ispenetrated on a reticle 540 by projection light. The fourth objective542 is used for projecting the area delimited by the knife edges intothe mask plane 540.

Optionally, a glass rod (not shown) for beam homogenization can beinserted between the third objective 534 and the mask device 538.

The exit pupil of the entire illumination system 510 is designated inFIG. 8 with reference numeral 560. All pupil planes 530, 550 of theillumination system are conjugated planes to the exit pupil 560. Theexit pupil 560 of the illumination system coincides with the entrancepupil of the projection objective 570 which projects the reticle 540onto a light-sensitive object 564 in an object plane 562.

The light-sensitive object 564 can be a semiconductor wafer coated witha light-sensitive layer.

An objective as described in the published application DE 10151309 isused as a projection objective. The scope of disclosure of thisapplication is hereby fully included in the present application; thatis, the entire disclosure of published application DE 10151309 isexpressly incorporated by reference herein.

FIGS. 9 a to 9 b show an example for a dipole-like pupil illumination asoccurs in an illumination system as shown in FIG. 8 a in the exit pupil560 which is conjugated to the pupil plane 550. FIG. 9 a shows anasymmetric pupil illumination in the exit pupil 560 which has not yetbeen corrected by the filter element in accordance with the invention.FIG. 9 b shows the position of a filter element inserted into the beampath, which filter element is located at a distance in accordance withthe invention in front of the pupil plane and therefore only causes apartial shadow. Moreover, the thus produced local reduction in intensityis shown, which on its part produces the symmetry of the pupilillumination in the exit pupil 560. Notice must be taken that thisconcerns a strongly simplified example, because filter devices arepossible in the present invention which include 10, possibly 20 and moreindividually controllable filter elements as shown in the FIGS. 2 to 7.

It is possible to position the filter device not in the pupil plane, butrather outside thereof, i.e. close to the pupil plane at a distance Δz.In this case partial shadow effects occur. As a result of an arrangementonly close to the pupil plane, an only very low influence is taken onthe shape of the pupil. On the other hand, the necessary brightnesscorrection is achieved in order to correct the asymmetry of the pupils.An arrangement of the filter device in accordance with the inventionclose to a pupil plane is therefore possible. It is also possible not toprovide all filter elements of a filter device in one plane. This meansthe individual filter elements can have a distance relative to eachother in the direction the beam propagates. As a result of this measure,selected filter elements can be associated with a predetermined partialshadow area. In accordance with the further development of theinvention, the filter elements can be displaced individually in thedirection of the beam in order to have a variable possibility foradjustment of the partial shadow which is individual to each filterelement.

FIG. 10 shows an embodiment of the invention with sensors arranged onthe rod-like filter elements 1003.1, 1003.2, 1003.3, 1003.4, 1003.5,1003.6, 1003.7,1003.8.

In the rod-like filter elements 1003.1, 1003.2, 1003.3, 1003.4,1003.5,1003.6, 1003.7,1003.8, the sensor is each arranged at the end1004.1, 1004.2, 1004.3, 1004.4, 1004.5,1004.6, 1004.7,1004.8. In therod-like filter element 1003.3, the entire rod-like filter element isprovided with sensors 1005.3.1, 1005.3.2, 1005.3.3, 1005.3.4, 1005.3.5,1005.3.6, 1005.3.7,1005.3.8.

The sensors 1005.1, 1005.2, 1005.3.1, 1005.3.2, 1005.3.3, 1005.3.4,1005.3.5, 1005.3.6, 1005.3.7, 1005.3.8, 1005.4, 1005.5, 1005.6, 1005.7,1005.8 allow the measurement of intensity values in the illuminatingbeam path along the filter element in a location-resolved manner. Themeasured intensity values of the filter element allow drawingconclusions on the influence of the filter element on the illuminationproperties of ellipticity, telecentricity and transmission.

FIG. 10 further shows a control device 1010 which is configured as apersonal computer and which in the illustrated case is connected byleads 1012.1, 1012.2 with the sensors 1005.1, 1005.8.

The intensity values measured with the sensors 1005.1, 1005.8 can beread into the control device 1010 and can be compared with the setpointvalues of an illumination to be achieved in the field or pupil plane.These setpoint values then lead to the setpoint positions for the filterelement to achieve the illumination in the field and/or pupil plane. Therod-like filter elements can then be brought to the respective setpointposition by the actuating elements (not shown in FIG. 10) as a result ofthis measurement.

The sensors 1005.1, 1005.2, 1005.3.1, 1005.3.2, 1005.3.3, 1005.3.4,1005.3.5, 1005.3.6, 1005.3.7, 1005.3.8, 1005.4, 1005.5, 1005.6,1005.7,1005.8 can be configured as power sensors, e.g. photodiodesensors, for determining the intensity values.

In the rod-like filter element 1005.3, the rod-like filter element iscovered completely with quasi punctiform power sensors. The sensors1005.3.1, 1005.3.2, 1005.3.3, 1005.3.4, 1005.3.5, 1005.3.6,1005.3.7,1005.3.8 are configured as a line of photodiode sensors or CCDline. Such a configuration comes with the advantage that the measurementof the absorbed intensity which depends on the location of the rod-likefilter element can occur in the filter element displaced into theilluminating beam path.

Since the power sensors are only required for determining the preciseposition of the filter element, it is provided for in a furtherdeveloped embodiment in order to protect the sensors from permanentradiation by the same illuminating mode that the filter element can berotated about its own axis in order to position the sensors in theshadow of the filter element after the performed measurement by turningthe filter element by 180° and thus to protect the sensors from damage.

The illustrated filter apparatus according to FIG. 10 in which therod-like filter elements are equipped with power sensors can, asdescribed above, be used as a filter element for the illumination of thepupil plane. It is also possible to arrange the filter element in such away that the illumination in a field plane is corrected by the pupilfilter element in accordance with the invention.

In order to avoid any overdrive of the range of dynamics of the diodewhen using photodiode sensors as sensors, it can be provided for in anembodiment of the invention that there is a variable attenuator afterthe light source, e.g. the laser light source, and before theilluminating optics.

While this invention has been described with respect to at least oneembodiment, the present invention can be further modified within thespirit and scope of this disclosure. This application is thereforeintended to cover any variations, uses, or adaptations of the inventionusing its general principles. Further, this application is intended tocover such departures from the present disclosure as come within knownor customary practice in the art to which this invention pertains andwhich fall within the limits of the appended claims.

The invention claimed is:
 1. An illumination system having a pupil, theillumination system comprising: a filter device, wherein: the pupil isilluminated with light during use of the illumination system; during useof the illumination system, the filter device corrects an intensitydistribution in the illumination of the pupil without influencing a sizeof the pupil; and the illumination system is a lithographic illuminationsystem.
 2. The illumination system of claim 1, wherein the filter deviceis upstream of the pupil along a path of the light in the illuminationdevice.
 3. The illumination system of claim 1, wherein the filter deviceis arranged in or close to a pupil plane of the illumination system. 4.The illumination system of claim 1, wherein, during use of theillumination system, the filter device reduces an ellipticity in anillumination angle distribution in the pupil without influencing a sizeof the pupil.
 5. The illumination system of claim 1, wherein, during useof the illumination system, the filter device reduces an ellipticity inan energy distribution in the pupil without influencing a size of thepupil.
 6. The illumination system of claim 1, wherein the filter devicecomprises a plurality of filter elements.
 7. The illumination system ofclaim 6, wherein at least some of the plurality of filter elements arerod-shaped.
 8. The illumination system of claim 6, wherein the filterdevice has an outside circumference, and the plurality of filterelements are arranged substantially in a radial direction with respectto the outside circumference.
 9. The illumination system of claim 6,wherein the filter device has a circular outside circumference with acenter, and each of the plurality of filter elements is moveable in aradial direction towards the center of the outside circumference. 10.The illumination system of claim 6, wherein at least some of theplurality of filter elements include a transparent region.
 11. Theillumination system of claim 6, wherein at least some of the pluralityof filter elements have a region that is an unsupported net structure.12. The illumination system of claim 6, wherein, for at least some ofthe plurality of filter elements, the filter element has a width and alength that is different from the width.
 13. The illumination system ofclaim 6, wherein at least some of the plurality of filter elements aremovable in a radial direction relative to a path of the light at thefilter element.
 14. The illumination system of claim 6, wherein, for atleast some of the plurality of filter elements: the filter element isconfigured to turn about an axis which is substantially radiallyoriented relative to a path of the light at the filter element; and thefilter element is displaceable an axis in an axial direction relative tothe path of the light at the filter element.
 15. The illumination systemof claim 1, wherein the filter device comprises more than 10 filterelements.
 16. The illumination system of claim, 1 wherein: the filterdevice is arranged in a distance region Δz relative to the pupil plane;a first boundary of the distance region is given by the pupil plane; asecond boundary of the distance region is given by a ΔZ_(max); andΔZ_(max) is defined in so that, at or near the pupil plane, partialshadows of the filter elements overlap by at most half in acircumferential region of the beam.
 17. The illumination system of claim1, further comprising an actuating device configured to change aposition of the filter element.
 18. The illumination system of claim 1,further comprising a sensor supported by the filter element, the sensorbeing configured to determine at least one property of the illumination.19. The illumination system of claim 1, further comprising sensorsconfigured to measure intensity values of the light in alocation-resolved manner.
 20. The illumination system of claim 19,wherein the intensity values of the light comprise at least oneparameter selected from the group consisting of an ellipticity of thelight, a telecentricity of the light, and a transmission of the light.21. A projection exposure system, comprising: an illumination systemaccording to claim 1; and a projection optics, wherein the projectionexposure system is a lithographic projection exposure system.